The objective of this proposal is to elucidate the control mechanisms of estrogen-induced luteolysis in domestic animals. The hypothesis developed is that an interaction exists between prostaglandin F2 alpha (PGF2 alpha) and estrogens which results in luteolysis. This hypothesis is based, in part, on observations of elevated plasma estrogen levels following PGF2 alpha treatment in cattle, the failure of PGF2 alpha to cause luteolysis after selective destruction of ovarian follicles in ewes, and the reduced efficacy of estradiol, but not PGF2 alpha, in causing luteolysis in hysterectomized sheep and cattle. The hypothesis is to be tested by experiments designed to determine the dependence of the luteolytic action of PGF2 alpha on estrogens and by experiments designed to determine if the luteolytic action of estrogens is enhanced by PGF 2 alpha. The relative importance of the LH receptor, intracellular translocation of the estrogen receptor, m-RNA synthesis and increased lysosomal activity to estrogen-induced luteolysis is also to be determined.